Market research has shown that “softness” is a property of paper-based consumer products, such as facial tissue, bath tissue, paper toweling, paper napkins, and the like, as well as other non-paper-based consumer products. It has been found that softness is important to consumers in selecting and determining the quality and desirability of such products. Therefore, it is advantageous to be able to demonstrate the softness of such a consumer product to the consumer, as a way of making the product more desirable.
One method for quantifying softness has been to determine metrics that describe fibers that emanate from the surface of a web substrate. While the configuration of fibers emanating from the surface of a web substrate may exist in many forms (e.g., fiber ‘loops’ where both ends of a fiber are attached to the surface and the middle of the fiber is not, ‘free fibers’ where one end of the fiber is attached to the surface and the distal end is not, or other configurations of ‘free fibers’ where the central portion of the fiber is attached to the surface and both ends are not attached, etc.) it can be advantageous to understand the metrics of the so-called ‘free fibers.’ This understanding of ‘free fibers’ is generally directed to those fibers attached to the underlying web substrate at one end while the distal end or part of the fiber is removed from the surface or fibers where a central portion of such fibers are attached to the surface and one or both ends are not. These metrics are sometimes known to those of skill in the art as the ‘free fiber end’ number or the ‘fuzz-on-edge’ value.
One method for determining the free fiber end number involves the manual (i.e., optical) counting of the number of free fibers whose one end is visible and unattached to a substrate surface. While this subjective method may be sufficient in certain circumstances, the overall free fiber end number can be affected by the person doing the counting (e.g., random error, fatigue, etc.) as well as the need for value judgments based upon what is believed to be contained within the image. Additionally, experience has shown that it can take between sixty and ninety minutes to perform a single analysis using this manual method. While the method itself may produce reasonable data, it can be difficult to perform adequate quality assurance to verify the data generated.
Another method used to quantify free fibers involves estimating the ratio between the length of the profile that outlines the free fibers and the width of the samples tested to provide an average fuzz-on-edge value or amount of free fibers. Such a method is described in U.S. Pat. No. 6,585,855 B2.
A significant draw-back of the above-mentioned analyses is that these processes can only provide one metric for the free fibers on a sample. These methods are difficult to adjust in order to provide other sample-related metrics. In other words, different tests have to be completed using different testing techniques and possibly apparatuses in order to provide a more complete picture of the metrics associated with a particular sample or product.
Additionally, having a more dynamic method of demonstrating the softness of a consumer product, using easily understood methods and familiar test materials, is clearly desirable. Compressibility and free fibers both contribute to product softness but are very different properties of the substrate. However a significant drawback of using the compressibility measure to express softness is that the results of scientific compressibility testing, while perhaps easily understood by one who is literate in the art of materials testing or in mathematics, may not be understood by the average consumer in relation to the subjective perception of softness. An ideal method for demonstrating softness would use the consumer product in a manner easily understood and related to by consumers. Such a method could be filmed or photographed and then used in advertisements, or it could be carried out in the direct presence of consumers, as a live demonstration in a store or other public location.
Accordingly, one problem faced by sanitary tissue product manufacturers is how to improve (i.e., increase) the “softness” properties of the sanitary tissue products based upon an increase in the number of free fibers as measured according to the Free Fiber Test Method described herein without significantly increasing the lint as measured according to the Lint Test Method described herein to better meet consumers' expectations for more clothlike, luxurious, and plush sanitary tissue products.
Accordingly, there exists a need for sanitary tissue products, for example bath tissue products, that exhibit improved “softness” properties based upon an increase in the number of free fibers as measured according to the Free Fiber Test Method described herein to provide consumers with sanitary tissue products that fulfill their desires and expectations for more comfortable and/or luxurious sanitary tissue products, and methods for making such sanitary tissue products.